The present invention relates to pointing devices, and in particular to micro sticks.
Many different mechanisms have been used to detect movement of a joystick. One type of joystick uses potentiometers, with a joystick moving a wiper on the potentiometer. Other types of joystick have attempted to avoid any mechanical interaction to increase the joystick lifetime. For example, numerous types of optical joystick designs have been developed. Other joysticks use electromagnetic sensing, such as by using Hall-effect sensors. A number of joysticks are designed to use induction coils, with the amount of inductance varying and being detected by an electric circuit.
For example, U.S. Pat. Nos. 4,685,678 and 4,855,704 show induction coil joysticks. In U.S. Pat. Nos. 4,879,556 and 4,642,595, a transmitter coil is included on the stick of the joystick, and is surrounded by receiving coils. Another type of design is shown in U.S. Pat. No. 4,654,576, where a metal disk is attached to the stick, with coils mounted on different sides of it. The metal disk has a tapered bottom, and as the joystick is tilted, the disk will come closer to certain coils, changing the inductance, which can then be measured by an electric circuit.
A number of different electric circuit designs are used to measure the movement of electromagnetic joysticks. Examples of some patents which show using either differential detection, or illustrate the use of oscillators in electric circuits, are U.S. Pat. Nos. 4,305,007 and 4,685,678.
One type of pointing device which could be considered similar to a miniature joystick is a micro-stick which can be found in the middle of an IBM Thinkpad (.TM.) laptop computer. The micro-stick is used in the same manner as imbedded trackballs or touchpads on laptops to indicate cursor movement. Such micro-sticks have also been used in gamepads and on top of a mouse. Typically, force sensing resistors are used which are made of conductive rubber making a variable contact between electrodes that are printed on an isolating support. They sense the pressure of the microdisplacement when the user pushes on the micro-stick with the user's finger. A constraint applicable to micro-sticks which is not applicable to joysticks is the limited space in which to mount the micro-stick, creating a need for a compact sensing structure.